President Obama visited the southern border Tuesday to push for an overhaul of the immigration system, part of a renewed effort to shore up his standing among Latinos and paint Republicans as hostile to a minority group that is a growing force in U.S. politics.

In a speech at the Chamizal National Memorial, Obama also sought to link the challenge of illegal immigration with another major political concern: economic anxiety. He said immigration reform "is an economic imperative."

"One way to strengthen the middle class in America is to reform the immigration system so that there's no longer a massive underground economy that exploits a cheap source of labor while depressing wages for everybody else," he said.

The chances of passing an immigration bill are low, but the White House is taking high-visibility steps to show it is not abandoning a goal that has its roots in the 2008 campaign.

In his appearance, Obama said his administration has made great strides in stopping immigrants from illegally crossing the southern border, even as Republican critics say he can do more.

"We have strengthened border security beyond what many believed was possible," he said.

But he said that illegal immigration requires a "comprehensive" solution that would also provide a path to legal status for the 11 million people living illegally in the United States. He also made another pitch for the Dream Act, which failed in the lame-duck session of Congress in December.

The speech comes after a series of meetings between the president and various stakeholders and reform activists in the past months. It was heavily promoted by the White House on a range of social media platforms, and Obama made a campaign-like pitch for the crowd to visit the White House website to sign up in support of his call for reform.

With Obama actively running for reelection, Republicans have questioned the sincerity and timing of his immigration push. House Speaker John A. Boehner's office said it hasn't even heard from the White House on the issue, evidence that immigration is not a serious legislative priority.

White House aides have not released a timetable for passing a bill, nor have they put forward a draft that could be the basis for congressional action.

Rep. Lamar Smith (R-Texas), chairman of the House Judiciary Committee, said in a statement: "It seems President Obama has once again put on his campaigner-in-chief hat. The president's push to legalize millions of illegal immigrants is purely political. The president wasn't able to pass his version of immigration reform when he had large Democratic majorities in the House and Senate because of bipartisan opposition."

Following the speech, Obama was to travel to Austin for a pair of fundraisers for his 2012 reelection campaign.